Regulation of Stroke Volume and Heart Rate Flashcards
what receptors does noradrenaline act on when increasing heart rate?
beta one receptors on the sinoatrial node
what effect does the parasympathetic system have on the sinoatrial node?
it acts on the muscarinic receptors hyperpolarising the pacemaker cells and decreasing the slope of the pacemaker potential, ultimately decreasing the heart rate.
what is the effect of increased venous return on the stroke volume?
it increases stroke volume as it results in an increased end diastolic volume, which is an increase in preload.
what is afterload?
this is the load against which the muscle is trying to contract
how is the stroke volume affected by an increase in total peripheral resistance?
increased TPR results in an increased afterload meaning a larger aortic pressure must be reached in the atrium before the valve opens. this means more energy is wasted reaching this pressure therefore decreasing stroke volume.
what happens if capacitance vessels are constricted?
the blood is pushed back to the heart, increasing EDV and preload resulting in a larger stroke volume.
how does the sympathetic system increase contractibility?
the nerves release noradrenaline that acts on beta 1 receptors on myocytes giving a stronger but shorter contraction.
why does the parasympathetic system have little effect on the contract ability?
the vagus nerve does not innervate the ventricular muscle
what is the effect of hypercalcemia on stroke volume?
there is an increase in stroke volume for a smaller EDV
what is the effect of hypocalcemia on stroke volume?
there is a decrease in stroke volume for the same EDV
what is the effect of ischaemia on the regulation of stroke volume?
this shifts the curve down and to the right, a smaller stroke volume for the same EDV as the loss of blood supply to the heart leads to less working muscle
what does cardiac output equal?
heart rate times stroke volume
why does increasing heart rate with an electronic pacemaker cause a small increase in CO but a decrease in stroke volume?
the shortened cardiac interval cuts into the rapid filling phase reducing the end diastolic volume therefore reducing preload. this by starling law then reduces the stroke volume
what increases the contractility?
increased sympathetic tone
what is the affect of increasing the contractility?
this alters the inotropic state and shortens the systole
